The Matchstick Castle by Keir Graff

Brian can think of a few places he'd rather spend his summer than with his aunt and uncle in Boring, Illinois. Jail, for example. Or an earplug factory. Anything would be better than doing summer school on a computer while his scientist dad is stationed at the South Pole.

Boring lives up to its name until Brian and his cousin Nora have a fight, get lost, and discover a huge, wooden house in the forest. With balconies, turrets, and windows seemingly stuck on at random, it looks ready to fall over in the next stiff breeze. To the madcap, eccentric family that lives inside, it's not just a home--it's a castle.
Suddenly, summer gets a lot more exciting. With their new friends, Brian and Nora tangle with giant wasps, sharp-tusked wild boars, and a crazed bureaucrat intent on bringing the dangerously dilapidated old house down with a wrecking ball.

Dog Gone Note: This book is in very good condition.